"Sir I dont get it what good is a knife in a nuke fight you just gotta press a button... sir."
"Cease fire.. Put your hand on that wall soilder... PUT YOUR HAND ON THAT WALL."
Soilder Puts hand on wall
Sergent Throws knife throw hand
"The enemy cannot press a button if you disable his hand.... Medic"

Yeah, but it's not like the enemy is going to conveniently place their hand on the wall for you to nail it with a knife. Also, if you have an M16 with you, I doubt most soldiers would have the guts to decide to knife the guy. That happens only in CS.

Na, you wouldn't knife him. All logic contradicts it.
Your survivablity chance decreases the moment you think about going for the knife. The chances of disabling the enemy decreases.
The display after the action is also less graphical.
You will probably lose more energy.
Also, if it turns out that the guy has friends, you're probably screwed.

DAMN YOU WHY DID YOU HAVE TO SAY IT!!!! YOU COULDNT WAIT A DAY OR UNTIL I GOT BACK FROM SCHOOL. I JUST GOT HERE SAW YOUR FIRST POST AND THEN WAS LIKE THATS FROM ZELDA AND YOU COULDNT WAIT TILL I GET HERE AHHHHHHHH